A main circuit breaker is used on Type A, C, and D services. Type T services do not have a main breaker. The main breaker size is based on the size of the load as computed according to the NEC. Since TxDOT standard services are 3 wire single phase, the main breaker always has 2 poles.

It is recommended to use the smallest size main breaker allowed by the load and the NEC, with a minimum of 60 amps. For the types of breakers specified by DMS-11080, the smaller sizes can reduce the intensity of arc flash in a service cabinet in case of accidental ground faults or short circuits